Conventional high-temperature alloys are strengthened mainly by solid solution and precipitation mechanisms that hinder dislocation movement. As the desired service temperatures become increasingly higher and the service life becomes significantly longer, these alloys can eventually lose their strength as the precipitates become dissolved or coarsened, and the solid solute atoms become highly diffusive due to the greatly increased thermal agitation.
The oxide dispersion strengthened (ODS) alloys, on the other hand, derives its high temperature strength mainly from a fine dispersion of oxides that are nearly insoluble in the matrix. This insolubility enables the oxide particles to hinder dislocation movements and thus retain strength up to temperatures near the matrix melting point. Furthermore, unlike precipitation strengthening, which requires high solubility of solute atoms at high temperatures and vice versa, the ODS mechanism is free from this temperature solubility requirement.
However, the oxide dispersion strengthened (ODS) alloys have their own disadvantage in joining. The strengthening oxide particles can only be “mechanically alloyed” into the metallic matrix through powder metallurgy. Bulk melting in fusion welding of the oxide dispersion strengthened (ODS) metal inevitably destroys the fine particle distribution by causing particle aggregation as the strengthening oxide particles are rejected at the solidification front in the weld pool, thus resulting in substantial decrease in high temperature strength of the weld.